diff --git a/packages/netlify-cms-core/index.d.ts b/packages/netlify-cms-core/index.d.ts
index 29f71eb3..26b5612c 100644
--- a/packages/netlify-cms-core/index.d.ts
+++ b/packages/netlify-cms-core/index.d.ts
@@ -429,7 +429,7 @@ declare module 'netlify-cms-core' {
     name: string;
     controlComponent: ComponentType<any>;
     previewComponent?: ComponentType<any>;
-    globalStyles: any;
+    globalStyles?: any;
   }
 
   export interface CmsWidget {